The invention is in the field of high intensity HMI lamps such as the kind used in movie sets and television lighting and in a number of other applications. Typically, these lamps are arc lamps in which the electrodes are surrounded by Argone gas at low pressure and a combination of mercury and rare earth elements. The temperature inside the lamps gets extremely high, and the light produced is quite intense, approximating the spectrum of sunlight. Bright colors are brought out very well by the lamp because of its high intensity and spectral distribution.
Because the lamps are so intense and run so hot, there life span is somewhat limited. The tungsten which is used in the electrodes evaporates and slowly coats the interior surface of the enclosing glass envelope, which further increases the heat by absorbing and reflecting the light rather than letting it pass through the glass. Thus as the lamp gets older, its deterioration accelerates.
Because in virtually all applications the light from this median point source lamp is required to be directed in a single beam of collimated or converging light, these lamps virtually always have a rear reflector so that rearwardly directed light is not lost. Reflectors in current practice are simple spherical mirror having its center of curvature at the lamp point-source. This arrangement, in a geometrically perfect model, reflects most of the rearwardly directed light back approximately along its incident path, so that it passes back through the point-source again in the forward direction. All reflectors in use are spherical. The trouble with this is that the light that is so reflected has already escaped the quartz envelope of the lamp once, but by being so reflected, the light passes again across the quartz envelope barrier once into the lamp and once again back out of the lamp at its forward side. Reflecting the light along this path needlessly further heats the lamp, and dissipates further the radiation which is needed forwardly in the lamp.
In another system which substantially avoids the above stated problem the generally hemispherical reflector has axial aperture and the lamp, which has two lateral arms, is oriented with its transverse axis, through the lateral arms, coincident with the axis of symmetry of the reflector. One arm of the lamp passes back through the axial hole in the reflector, and the result is that none of the light, or substantially none of the light, is re-directed through the light source portion of the lamp.
However, this arrangement suffers from another drawback. The lamp must be mounted and suspended by the ends of its lateral arms, and thus, although not shown in drawings, the yolk and electrical connection to the ends of the arms interferes with light passage near the forwardly-directed arm. Thus although the reflected light successfully circumradiates the intense center of the lamp, nonetheless it loses a portion of its radiation by absorption and scattering off of the front portion of the mounting and energizing yolk. Even beyond this, in many applications it is desirable and perhaps an absolute necessity to mount the lamp in a transverse arrangement rather than a longitudinally aligned with the reflector axis.
There is a need therefore for a reflector arrangement that can accommodate a transversely extended high intensity lamp, having its transverse axis substantially perpendicular to the reflector axis, and yet reflect the rearwardly directed radiation from the lamp back forwardly in such a way that it passes by the lamp rather than re-penetrating the fiery core of the quartz envelope.